Mark bad Content-Length tests as pending for Go 1.2

This was a regression found when compiling and testing the router
under go 1.2 compared to 1.1.2 (currently built against version).
Since go 1.2 the behaviour for how bad Content-Length headers are
handled has changed from providing a (private) error value that we
could match against through to directly returning an
`io.ErrUnexpectedEOF` error.

Marking these tests as pending as they may eventually start working again
and somebody should look at it again when that happens.
Merge pull request #70 from alphagov/return-500-response-for-bad-content-length-in-go-1.2

Mark bad Content-Length tests as pending for Go 1.2